Molding method for making plastic foam-backed shells

ABSTRACT

A method of molding a plastic shell having an outer pliable skin layer and a foam backing layer comprises casting a first skin layer portion from wear resistant material in a first casting sequence for those areas of the panel susceptible to high wear and in a second casting sequence casting self-skinning foamable material against the remaining portion of the mold surface and over the first-cast skin layer portion to develop, simultaneously, the remaining outer skin layer portion of the shell and a foam backing layer which extends across the entire skin layer.

This invention relates to a method for molding a single-piece plasticshell having a pliable outer skin layer backed by a soft foam layer.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,238, 622 discloses a method for molding a plastic shellfrom a self-skinning foamable thermoplastics material which, when castagainst a heated mold surface, produces a non-porous outer skin layerbacked by a thin layer of soft foam material. The concurrent developmentof the skin and foam backing layers simplifies the manufacturing of theshell by combining what otherwise would be separate steps in theformation of the skin layer and foam backing layer. It has been foundthat when the skin layer portion of the shell is made very thin (i.e.,on the order of 0.001 inches to 0.010 inches) and somewhat porous, thatthe panel exhibits a desirable tactile gripping quality that is verypleasing to the touch making it desirable for use in automotive interiorapplications such as door panels, arm rests, and the like. However, ithas further been found that such a thin and porous skin layer is farless durable and wear resistent than conventional dense and non-porousskins frequently used in such applications, such as the materialsdisclosed in U.S. Pat. No. 4,562,025.

A foam-backed plastic shell formed in accordance with the presentinvention overcomes the foregoing objections.

SUMMARY OF THE INVENTION AND ADVANTAGES

A method of molding a plastic shell having an outer pliable skin layerand a foam backing layer includes providing a charge of wear resistantmaterial and a separate charge of self-skinning foamable material. In afirst casting sequence, the wear resistant material is cast against onlya portion of a heated mold surface of a casting mold to form afirst-cast portion of the shell's outer skin layer. In a subsequentcasting sequence, the self-skinning foamable material is cast againstthe remaining portion of the mold surface still exposed after the firstcasting sequence and over the first-cast portion of the outer skin layerto generate simultaneously a remaining portion of the outer skin layerthat is united to the first-cast portion thereof and an integral foambacking layer that extends across the entire skin layer of the shell.

A primary advantage of the present invention is that the majority of theshell can be made from the self-skinning foamable material Laving anouter skin layer that exhibits the tactile e gripping quality desirablein automotive interior trim applications discussed above. In thoseregions of the shell susceptible to high wear, such as the tops of armrests and other areas contacted frequently by the user or objectssupported by the shell, such as cup holders, trays, and the like, arelatively greater wear resistent (preferably non-foaming for thegreatest wear resistance) material can be employed to provide the skinlayer in such high wear regions of the shell.

The present method retains the advantages provided by the self-skinningfoamable material in eliminating the need to first form an outer skinlayer and then a separate foam backing layer in separate operations,while overcoming the wearability disadvantages of a thin skin layer ofsuch self-skinning foamable material by incorporation of a relativelymore durable skin layer portion of wear resistant material in regions ofthe panels susceptible to high wear.

According to yet another advantage of the invention, the wear resistantmaterial can be colored differently than the self-skinning foamablematerial to generate a one-piece multi-color skin layer on the shell.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages and features of the invention will becomemore readily apparent and appreciated by those skilled in the art fromthe following detailed description and accompanying drawings wherein:

FIG. 1 is a diagrammatic view of a single-piece multi-material shellprepared in accordance with the present invention shown with associatedcomponent parts of an automotive vehicle door panel;

FIG. 2 is a diagrammatically shown cross-sectional view of a moldcomponent for use in practicing the present invention;

FIG. 3 is a diagrammatically shown sectional view of a partitionedcharge box coupled to the mold of FIG. 2 in a pre-release position;

FIG. 4 is a cross-sectional view like FIG. 3 but with the mold toolinverted to a powder-release position to carry out a first castingsequence of the present molding operation;

FIG. 5 is a diagrammatic cross-sectional view like FIG. 3 but showing asecond unpartitioned charge box coupled to the mold following thecasting of a first skin layer portion on the mold;

FIG. 6 is a view like FIG. 5 but with the mold tool inverted to apowder-release position; and

FIG. 7 is a fragmentary, enlarged sectional view of a multi-materialshell prepared by the process of the present invention.

DETAILED DESCRIPTION

The process, apparatus, and article of the present invention will bedescribed with reference to the production of plastic single-piece thinwalled shells for a typical automotive interior trim part, such as aninterior door panel, consoles, arm rests, and instrument panels.

FIG. 1 shows a typical automobile door panel application of asingle-piece, multi-material interior plastic shell 10 prepared inaccordance with the present invention. The shell 10 includes an outerpliable skin layer 12 of plastics material backed by an integratedplastic foam layer 14. The plastics materials for either layer may bethermoplastic or thermoset in nature. An interior reinforcing insert 16is joined to an exterior door panel 18 to provide an interior space 20therebetween to accommodate the raising and lowering of a window 22.

FIGS. 2-6 illustrate powder molding apparatus and process for preparingthe shell 10 according to the present invention. However, the apparatuscould also accommodate use of the invention with either a liquid orpellet material media. FIG. 2 illustrates a powder casting mold 24having a heated mold surface 26. A first charge box 28 has an interiorpartition wall or divider panel 30 enclosing a containment area 32 ofthe box 28 in which a charge of wear resistant plastic material 34 isintroduced and the charge box 28 coupled by clamps 36 to the open-endedmold 24, with the mold 24 initially arranged above the charge box 28 ina pre-release position illustrated in FIG. 3. The free ends of thedivider wall 30 are sealed by inflatable gaskets 38 against the moldsurface 26 to isolate a predetermined portion 26a of the mold surface 26above the containment area 32 from the remaining portion 26b.

The closed system of FIG. 3 is then inverted to a mold-down positionillustrated in FIG. 4 causing the charge of wear resistant material 34within the containment area 32 to be cast against the partitioned area26a of the mold surface. In the preferred embodiment, the partitionedarea 26a of the mold surface represents a region of the shell that inuse is susceptible to high wear, such as the upper arm rest 42 and ledgeregions 44 and the door panel of FIG. 1. In other applications, suchhigh wear regions may include areas such as cup holders, shelf trays,and other areas designed to hold or come into frequent or prolongedcontact with containers or other objects.

Examples of suitable materials for the wear resistant materials 34include thermoplastic powders such as plasticized polyvinyl chloridesand related vinyl resins supplied in dry powder form for ease of gravityflow out of and into the charge box 28 of the types presently used bythe industry in a manufacture of plastic shells for door panels, armrests, instrument panels, consoles, and the like prepared byconventional PVC powder molding processes. U.S. Pat. No. 4,562,025discloses such suitable thermoplastic powders that may be used for thewear resistant material 34 in carrying out the present invention, thedisclosure of which is incorporated herein by reference. Other plasticmaterial groups may include urethanes, olefins, olefin elastomers,polyesters, styrenics, and rubbers.

As the wear resistant material 34 is cast against the mold surfaceportion 26a, the heat from the mold melts the material adjacent the moldsurface to form a cast layer 46 of the wear resistant material. Thedwell time and mold temperature can be adjusted to control the thicknessof the layer 46. The mold 24 is then cooled to cure the layer 46 of thewear resistant material which adheres to the mold surface 26a. The mold24 along with the charge box 28 is inverted to the mold-up positiondumping any excess unfused material 34 back into the charge box 28, andthe box 28 is unclamped from the mold 24.

A second charge box 48 is then attached to the mold 24 to define aclosed system in which the entire mold surface 26 is exposed to theinterior of the second charge box 48, including the first skin layerportion 46, as illustrated in FIG. 5. Prior to attaching the secondcharge box 43, a charge of self-skinning foamable material 50 isintroduced into the charge box 48. The mold 24 and box 48 are theninverted to the mold-down position illustrated in FIG. 6 causing theself-skinning foamable material 50 to be cast against the remainingexposed portion 26b of the mold surface not previously covered by thefirst layer 46 of material as well as across the exposed back side ofthe pre-cast first layer 46.

Suitable plastics that can be used to make up the charge ofself-skinning foamable materials 50 are disclosed in U.S. Pat. No.5,238,622, commonly owned by the assignee of the present invention andits disclosure incorporated herein by reference. The preferred blendratio is 75% by weight of a dry powder polyvinyl chloride foam compoundhaving a relatively high molecular weight blended with a foaming agent,as identified in the '622 patent and 25% by weight of a secondrelatively lower molecular weight polyvinyl chloride thermoplastic drypowder compound prepared according to the teachings of the '622 patent.The high and low molecular weight portions are blended together in theprescribed ratio and, when cast against the mold surface portion 26b andacross the first skin layer portion 46, the lower molecular weightmaterial, having a lower melting point, are caused to melt and form athin and somewhat porous skin portion 52 across the exposed mold surfacearea 26b, forming an integral joint with the precast first layer portion46, such that the portions 46 and 52 together define the unitary outerskin layer 12 of the shell. The remaining lower melting point materialinteract with those of the 75% portion to form, simultaneously with thedevelopment of the skin layer portion 52, an integral closed cell foambacking layer 54 extending across the entire skin layer 12 of the shell10, including the first and second skin layer portions 46, 52 of thepanel, as illustrated in FIG. 7.

As mentioned, the skin layer portion 52 is preferably thin and somewhatporous, which provides the material with a desirable tactile grippingfeel which is pleasing to the touch. The thickness of the skin layerportion 52 is preferably in the range of 0.001 inches to 0.10 incheswhich attributes to the porous nature of the portion 52 and gives it itscharacteristic soft, gripping feel.

During casting of the portion 52, the low molecular weight material meltpools around the higher molecular weight material and flow against theheated mold surface portion 26b. The higher molecular weight materialreacts with the foaming agent to form the closed cell foam backing layer54. The mold is cooled to room temperature and the resultant shell 10removed from the mold 24.

Although the thin and relatively porous outer skin layer portion 52produces the desirable gripping sensation to the touch, its thinness andporosity detracts from the wearability of the material, thus the reasonfor providing the first skin layer portion 46 of the wear resistantmaterial for high wear sections 42 and 44. The layer portion 46, by itsnature, exhibits relatively greater wear resistance characteristics andcan be developed to a greater thickness than that of the surroundingskin layer portion 52, as illustrated in FIG. 7, further adding to itswearability and suitability for sections 42 and 44.

Alternatively, the wear resistant skin layer 46 may be formed by methodsother than casting. The layer 46 may be sprayed onto the mold surface26a of mold 24. The spray may comprise plastic material, such as powderor liquid, appropriately engineered to be sprayed by known spray guns.The mold surface 26a may be preheated or heated after the plastic issprayed onto the mold surface 26a to form the layer 46 and then cooledto cure layer 46. For example, preheating of the mold to temperaturestypical for casting would not be required for the spray application of athermoset urethane. The thermosetting reaction of the urethane could beaccommodated through various chemistry changes as is well known in theart as a means to promote proper cure of the material without having torely on typical casting temperatures for adequate cure. The remainingself-skinning foaming material may be applied as described above and asshown in FIGS. 5 and 6.

If desired, the wear resistant material that produces the first skinlayer portion 46 can be colored differently than the self-skinning,foamable material used to generate the remaining skin layer portion 52such that a single-piece multi-color skin layer 12 results. On the otherhand, the charge materials 34 and 50 can be selected to have the samecolor such that the relatively more durable first skin layer portion 46is visibly imperceptible from the surrounding remaining skin layerportion 52 in the final product.

While the invention is described with reference to the manufacture of ashell having a self-skinned outer skin layer portion which is relativelythin and porous so as to exhibit a desirable gripping quality, it issuitable for use in the formation of other shells of the same generaltype but whose outer skin layer portion is developed to be relativelythicker and non-porous, but yet combined with an outer skin layerportion of wear resistant material exhibiting relatively greater wearresistance than the surrounding self-skinning outer layer materialprovided in those areas of the panel susceptible to high wear.

The disclosed embodiments are representative of a presently preferredforms of the invention, but are intended to be illustrative rather thandefinitive thereof. The invention is defined in the claims.

We claim:
 1. A method of molding a plastic shell having an outer pliableskin layer and a foam backing layer, said method comprising the stepsof: providing a charge of self-skinning foamable plasticsmaterial;providing a charge of wear resistant plastic material whichforms a skin layer portion which is relatively more wear resistant thanthe skin layer portion of the self-skinning foamable material; providinga casting mold having a heated mold surface; forming the wear resistantplastic material against a predetermined portion of the mold surfaceleaving the remaining portion of the mold surface exposed to generate afirst portion of the outer skin layer of the shell; and casting theself-skinning foamable material against the exposed portion of the moldsurface and across the first portion of the outer skin layer tosimultaneously generate a remaining portion of the outer skin layerunited to the first portion of the skin layer and an integral foambacking layer extending across the entire skin layer of the shell; andwherein the first portion of the outer skin is formed by casting andincludes partitioning the predetermined portion of the mold surface fromthe remaining exposed portion during casting of the wear resistantmaterial to contain such material within the predetermined region of themold surface; and further including removing the partition following thecasting of the wear resistant material and casting the self-skinningfoamable material across the entire mold surface.
 2. The method of claim1 wherein the wear resistant plastic material comprises a vinylcompound.
 3. A method of molding a single-piece plastic shell having apliable outer skin layer backed by a foam layer, said method comprisingthe steps of:providing an open-ended casting mold having a heated moldsurface; providing a first charge box having an interior partition wallenclosing a containment area and introducing into the containment area awear resistant plastic material; providing a second unpartitioned chargebox and introducing into the second charge box a self-skinning foamablemixture of relatively high molecular weight plastic material andrelatively lower molecular weight plastic material having differentmelting properties and a foaming agent blended with the high molecularweight material; in a first casting sequence, coupling the first chargebox to the mold to form a closed system in which the interior partitionwall of the charge box is sealed against the mold surface to isolate aportion of the mold surface and casting the wear resistant material ontothe isolated portion of the mold surface only to form thereon afirst-cast portion of the outer skin layer from the wear resistantmaterial, and thereafter uncoupling the first charge box from the mold;and in a second casting sequence, coupling the second charge box to themold to form a closed system and casting the self-skinning foamablemixture against the remainder of the mold surface and over thefirst-cast portion of the skin layer and activating the mixture to formsimultaneously therefrom the remaining portion of the outer skin layerunited to the first-cast portion and an integral foam backing layerextending across the entire skin layer of the shell.
 4. The method ofclaim 3 wherein the wear resistant plastic material is selected from thegroup consisting of urethane, olefins, olefin elastomers, polyesters andstyrenics.
 5. The method of claim 3 wherein the self-skinning foamablemixture material comprises a vinyl compound.
 6. The method of claim 5wherein the vinyl compound is polyvinyl chloride.